rename resource nitb_iface to ip_address

I would like to use the IP addresses also for OsmoBSC processes, so it is more
than clear now that 'nitb_iface' was the wrong naming choice.

The only distinction we may need in the future is public versus loopback
interface. To add that, we may add a trait to the 'ip_address' resource
like:

  ip_address:
  - addr: 10.42.42.1
    type: public
  - addr: 127.0.0.1
    type: loopback

This way we can substitute public vs loopback addresses flexibly (e.g. using
scenarios).

Change-Id: I3ad583ae7a33f7a7bb56fe78a125f73c56a0e860
diff --git a/selftest/resource_test.py b/selftest/resource_test.py
index 2d0f880..08f1fbf 100755
--- a/selftest/resource_test.py
+++ b/selftest/resource_test.py
@@ -72,7 +72,7 @@
 
 print('- request some resources')
 want = {
-       'nitb_iface': [ { 'times': 1 } ],
+       'ip_address': [ { 'times': 1 } ],
        'bts': [ { 'type': 'sysmo', 'times': 1 }, { 'type': 'oct', 'times': 1 } ],
        'arfcn': [ { 'band': 'GSM-1800', 'times': 2 } ],
        'modem': [ { 'times': 2 } ],